THE FERTILIZATION PROCESS IN THE SNAIL. 79 



fore it was entirely out of the snail's body, pulled out and im- 

 mediately fixed. Sections of these eggs were found in various 

 stages of the first maturation division. Further proof of ir- 

 regularity of maturation is shown in two eggs which were found 

 in advanced cleavage stages in the hermaphrodite duct of dif- 

 ferent snails (Figs. 17, 18). The maturation divisions come sur- 

 prisingly near being synchronous in all the eggs of a given mass, 

 the laggards being usually those at the ends of the mass. Kofoid 

 ('95) found much variation in Lima.v eggs of the same mass. 



Conklin ('10, p. 420) seems to have found a germinal vesicle 

 regularly present in eggs of L. coluniella which had been ovi- 

 posited, for he says : "... As the germinal vesicle begins to dis- 

 solve and the first maturation spindle appears, the clear area of 

 the germinal vesicle becomes elliptical and then spindle-shaped in 

 outline." It is evident he is using the term " germinal vesicle " 

 to include all nuclear stages before the polar bodies are extruded, 

 for a true germinal vesicle, as defined by Purkinje, 1825 (Wilson, 

 '25) was not found in living or sectioned eggs laid by L. s. ap- 

 pressa. Since only one instance in which the germinal vesicle 

 persisted until the egg reached the hermaphrodite duct has been 

 found (Fig. 6) and since well-formed spindles occurred in sev- 

 eral eggs within the hermaphrodite duct (Figs, n, 12. 13, 15 and 

 1 6) I am of the opinion that in the eggs of L. s. apprcssa the 

 germinal vesicle has disappeared by the time the egg enters the 

 oviduct. 



My observations on the living eggs of both " virgin " and 

 " normal " L. s appressa are in accord with Conklin's work ('10) 

 inasmuch as the clear area " becomes elliptical, then spindle-shaped, 

 . . . then moves through the egg until one end of the elongated 

 area comes into contact with the surface at the animal pole of the 

 egg, leaving a deep ' well ' of clear protoplasm leading down to 

 the center of the egg." This " well " is the result of forces con- 

 nected with mitosis by means of which the yolk granules are dis- 

 placed, or almost so, thus leaving an apparently clear area in liv- 

 ing eggs, the " well," in which the first maturation spindle is 

 formed and subsequently migrates to the animal pole of the ovum 

 (Figs. 49, 51). A clear area forms similarly in the egg of the 

 worm Nereis (Lillie, '12) ; the echiuroid Thalasseina (Griffin, 



